The build system

Basic use

Basic use is described in development.md.

Architecture

The build/ folder is made up of 4 packages:

• build/configure defines the actions and inputs/outputs of the build graph - this is where you add new build steps or modify existing ones. The defined actions are converted at build time to a build.ninja file that Ninja executes.
• build/ninja_gen is a library for writing a build.ninja file, and includes various rules like "build a Rust crate" or "run a command".
• build/archives is a helper to download/checksum/extract a dependency as part of the build process.
• build/runner serves a number of purposes:
  • it's the entrypoint to the build process, taking care of generating the build file and then invoking Ninja
  • it wraps executable invocations in the build file, swallowing their output if they exit successfully
  • it provides a few helpers for multi-step processes that can't be easily described in a cross-platform manner thanks to differences on Windows.

Tracing build problems

If you run into trouble with the build process:

• You can see the executed commands with e.g. ./ninja pylib -v
• You can see the output of successful commands by defining OUTPUT_SUCCESS=1
• You can see what's triggering a rebuild of a target with e.g. ./ninja qt/anki -d explain.
• You can browse the build graph via e.g. ./ninja -- -t browse wheels
• You can profile build performance with https://discourse.cmake.org/t/profiling-build-performance/2443/3.

Packaging considerations

See this page.